Tracing lamprey's sense of smell important breakthrough for biologist

You might be tempted when you get a good whiff of chocolate, pizza or coffee, but always have the ability to make a conscious decision about whether or not you’ll indulge.

There are very few known examples of humans moving involuntarily in response to smells, but in the animal kingdom, it happens regularly. Dogs track odours over long distances and newborn mammals react to the scent of their mothers.

Now a UWindsor biology professor and her colleagues have made an important discovery by mapping out the neural route between a sea lamprey’s nose and its spinal cord, which helps explain why certain smells make the invasive creature automatically swim.

“There is a pathway in the olfactory system that goes directly to movement,” explained Barb Zielinski, who recently published her findings in the academic journal PLOS Biology. “We’ve identified a specific subsystem within the central nervous system that’s dedicated to producing motor responses to olfactory input. It tells us that a vertebrate brain can translate smell in to locomotion.”

The sea lamprey is a long, skinny, parasitic fish that’s considered a non-native invasive species in the Great Lakes. It preys on a variety of other species, using its suction-cup like mouth to attach itself to the side of a fish to feed on its tissue and blood, slowly killing its host.

In the sea lamprey, mating occurs after ovulated females are attracted to spawning sites by male sex pheromones, and Dr. Zielinski said this research proves that the lamprey’s movement can be activated by both food-related or pheromonal olfactory cues.

The research involved injecting dyes into the lamprey’s brain for following “neuronal trajectories,” as well as specialized activity indicator dyes for locating locomotor control cells that respond to odours, said Zielinski. She worked on the project with former graduate students Xiang Ren and Steven Chang, as well as Réjean Dubuc,a professor at L’Université de Montréal and L’Université du Québec à Montréal. The scientists also used electrophysiology—the measurement of electrical current in biological cells—to record how the lamprey’s neural cells reacted to olfactory cues. These experiments allowed them to trace the synaptic route the olfactory information followed from the lamprey’s brain to its spinal cord.

The findings, she said, suggest “a tight coupling between the olfactory system and brain areas controlling movements,” and are significant because they validate the work presently being done by conservation managers working with the Great Lakes Fishery Commission, who are using olfactory-based strategies to reduce the population of sea lampreys in the lakes. In a broader context, this study shows that olfactory input can directly affect movement.